Wow, pretty amazing that all that technology can fit into a single set of pedals, but these things really do reliably report power to a Garmin 800 cyclocomputer (if only getting the data out of that thing was as easy, but that's another post).
Note that these thing do take Lithium AA batteries, so order up some rechargeable and you should be pretty set.
Also the cleat themselves are kind of like Look Keos, but don't order the standard Look cleat covers, they are not quite wide enough. PowerTap recommends the Exustar E-CK1B cleat cover. Kirkland Bikes has them as does Planet Cyclery or just get them from a reputable reseller on Amazon.
They are accurate left/right, reliable and they are easy to move to different bikes since they are just pedals. but they are heavy adding a full pound to your kit. And they do use the single sided Keo pedals.
Alternatives a year later getting lighter
If you are really looking for the lightest option and you, like me, the super light Speedplay pedals and the dual entry that they offer then a better choice would be the systems that are built into the crank arms.
DC Rainmaker has a great overview of power meters that he personally has used. The emphasis is on reliable, Bluetooth and ANT and as light as possible.
Quarg Dzero was acquired by SRAM but does have reliable crankarm power meters that he uses regularly. however this is not a true left/right unit, although it is unclear if that really matters for most riding. It has about a 70 gram penalty.
The Shimano Dura-Ace R9100P crankset as an alternative. So it means it's more expensive but it is going to be light. They don't offer Bluetooth though but are just 70 grams over non power pedals. And they use a wire to connect the two sides which is prone to breaking. As is the recharging connector. Finally it does need a magnet rather than an accelerometer to determine spinning.
Powermax NG Eco is a good deal with a pod that goes into your chainring. Not clear on the weight penalty but relatively inexpensive.
Some other options are Stages or 4iiii which use a pod that you put onto your crank.
Stages LR just came out and is a dual leg option that adds just 35 grams to the whole setup even for dual left/right and the extended review shows that it works well for both DC Rainmaker and Bikeradar. The Dura-Ace 9100 option is $1300 but it does come with a whole crankset and the Ultegra R8000 is $1000. And the Dura-ace is lighter at 609 grams vs 674 grams, so in the end, going to this set if you are on Ultra now actually is 35 grams less than the Ultegra, although some of that is the lighter chain rings. They perform the same, so it is a tiny difference for the true weight weenie 🙂